1. Technical Field
The present invention relates to a stent for use in implantation in a patient and a fabrication method thereof, and more particularly to a stent which is self-expandable and can deliver drugs tropically, and a fabrication method thereof.
2. Background Art
Expandable medical prostheses, so-called stents, are known and commercially available. They are disclosed generally in U.S. Pat. No. 4,655,771 (Wallsten), U.S. Pat. No. 5,061,275 (Wallsten et al.) and U.S. Pat. No. 5,645,559 (Hachtmann et al.), for example. Stents are used within blood vessels for various medical applications. For example, there are intravascular stents for treating stenoses, and stents for maintaining openings in urinary, biliary, tracheobronchial, oesophageal and renal tracts and inferior vena cava.
Commonly used materials for known stent filaments are Elgiloy™ and Phynox™ metal spring alloys. Other metallic materials that can be used for expandable stent filaments include 316 stainless steel, MP35N alloy and superelastic Nitinol nickel-titanium. Another expandable stent disclosed in, for example, U.S. Pat. No. 5,630,840 to Mayer has a radiopaque clad composite structure. Expandable stents may be made of a titanium alloy.
For example, EP 1287790 (Schmitt & Lentz) discloses an axially flexible braided stent that is self-expandable due to the elastic memory of the braided polymer fibers. The braided fibers are shaped into a tube at or slightly below the melting temperature of the polymer, and then longitudinally stretched upon cooling.
To date, stents have been mainly hand-made and the productivity is significantly low. Also, such prior art stents are difficult to have uniform characteristics (elasticity and/or self-expandability) over their entire length. For example, prior art stents have irregular distances between metallic wires defined therein.
Alternatively, a braiding apparatus has been used to produce stents. Thus-produced stents, however, have a problem. That is, since the stents have at their end portions metal filaments the end portions of which are exposed, additional process is required to weld the exposed end portions of the metal filaments to each other. This problem is aggravated when a stent is composed of fine filaments having a relatively small diameter; from the practical point of view, it is almost impossible to weld the end portions of such a stent.
Korean Patent Application Publication No. 1999-45770, for example, suggests a technique for the purpose of solving the above-described problems, which discloses a stent in which beads are welded at the ends of filaments constituting a stent body. However, this technique still has problems. First, it is not easy to weld fine particles of beads to ends of the filaments having a fine diameter. Further, when welding of the beads is not perfectly performed, there can be undesirable exposure of a sharp tip portion of stents, which may damage blood vessels of a patient.